Re: cgroups(7): documenting cgroups v2 thread mode

[Michael Kerrisk (man-pages)]

On 01/09/2018 10:10 PM, Tejun Heo wrote:
> Hello,
> 
> On Tue, Jan 02, 2018 at 07:24:01PM +0100, Michael Kerrisk (man-pages) wrote:
>>        2. We write the string "threaded" to each of the domain invalid
>>           cgroups  under  y,  in  order  to  convert  them to the type
>>           threaded.  As a consequence of this step, all threads  under
>>           the  threaded  root  now  have  the  type  threaded  and the
>>           threaded subtree is now fully usable.   The  requirement  to
>>           write  "threaded"  to each of these cgroups is somewhat cumâ
>>           bersome, but allows for possible future  extensions  to  the
>>           thread-mode model.
>>
>>           âââââââââââââââââââââââââââââââââââââââââââââââââââââââ
>>           âFIXME                                                â
>>           âââââââââââââââââââââââââââââââââââââââââââââââââââââââ
>>           âRe  the preceding paragraphs... Are there other reaâ â
>>           âsosn  for  the  (cumbersome)  requirement  to  write â
>>           â'threaded'  to  each of the cgroup.type files in the â
>>           âthreaded subtrees? Tejun Heo mentioned  the  followâ â
>>           âing:                                                 â
>>           â                                                     â
>>           â    Consistency w/ the cgroups right under the root  â
>>           â    cgroup.  Because they can be both domains and    â
>>           â    threadroots, we can't switch the children over   â
>>           â    to thread mode automatically.  Doing that for    â
>>           â    cgroups further down in the hierarchy would be   â
>>           â    really inconsistent.                             â
>>           â                                                     â
>>           âBut,  it's  not  clear  to  me  how  "Doing that for â
>>           âcgroups further  down  in  the  hierarchy  would  be â
>>           âreally inconsistent", since in the current implemenâ â
>>           âtation, those same thread groups  are  converted  to â
>>           â"domain invalid" type.  What am I missing?           â
>>           âââââââââââââââââââââââââââââââââââââââââââââââââââââââ
> 
> Yeah, I was confused with an earlier varient where we were marking
> threaded domains instead of threaded roots.  It's mostly about future
> extensibility (especially as Waiman was proposing related changes
> there) and not doing things automatically / recursively if possible.
> 
> Looks good to me.

One more thing. I added the following sentence to the text:

       The  cgroup.threads file is writable only for the cgroups inside a
       threaded subtree.

Can you confirm that that is correct, please.

Cheers,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/